1. Field of the Invention
The present invention relates generally to data communication systems, and more specifically to data communication using a network DCE and a channel-associated signaling scheme. The present invention is particularly suitable for mobile computing using a cellular telephone.
2. Description of the Related Art
In conventional mobile data communication systems, the data circuit-terminating equipment (DCE) for a mobile use end system is located within the mobile switch center (or mobile telephone switching office) to serve as a local DCE, whereas fixed user end systems usually have their own DCE within the premises of the fixed users. An interworking unit is therefore provided in the mobile switching center for performing interworking operations between the local DCE and a destination DCE. The mobile switching center has a signaling controller that provides switching and signaling functions. The signaling controller is connected to the interworking unit via time-division multiplexed signaling channels associated respectively with time-division multiplexed data channels.
When a mobile user end system sends a REQUEST message to the mobile switching center, the signaling controller applies a SETUP message to the interworking unit to activate the local DCE. However, the signaling message of the channel-associated signaling is represented by a single bit, and there is no response message for the setting-up of the DCE. Therefore, the signaling controller would have to wait a longer period of time to return an acknowledgment than would be necessary. In addition, the local DCE must be set with parameters from the local mobile user. However, there is no response message for the parameter setting process. As a result, no data service is satisfactorily provided with the current data communication system where the channel-associated signaling scheme is used between the signaling controller and the interworking unit for controlling the local DCE.